Matching two-arm spiral impedance without balun

Abstract

Spiral antennas can be designed to cover decades of bandwidth (e.g. 350-8350 MHz). Connecting the antenna directly to the coaxial cable without a balun would reduce fabrication costs without sacrificing realized gain. This paper shows how two-arm spiral antennas can be designed to have a broadband impedance close to 50 Ohms, rather than the traditional 180 Ohms, without the need to make and attach a balun.